If you've ever had a production line stop at 2 a.m. because an actuator stopped moving, you know the first feeling isn't concern—it's panic. Then the second question arrives: what happens when a linear actuator fails, and where do you even start?

This checklist is for engineers, maintenance leads, and procurement people who need to respond to a failed linear actuator fast. Not the ideal-world version. The version where downtime is already ticking on a board. I've coordinated a lot of these calls over the years—maybe 200, maybe 180, I'd have to check my log—and the same sequence keeps working. It's basically: stop, confirm, verify, inspect, decide, test. Six steps.

Step 1: Stop, Lock Out, and Document the Failure

Before you touch anything, lock out the machine and take photos. Sounds obvious, but in a rush, people skip it. A photo of the failed axis position, the alarm text, and the controller display is worth more than a memory.

Write down:

  • What was the actuator doing when it failed—extending, retracting, holding, cycling?
  • What was on it at the time? A gripper, a tool, a door, a load.
  • Any fault codes or alarms? Screenshot them.
  • Was the machine running at high speed or just starting up?

Most buyers focus on the replacement part and completely miss the sequence of events. That's an outsider blind spot. The exactly wrong move is to reset and run again, because if the actuator failed under load, it will fail again.

Step 2: Measure the Voltage at the Motor, Not at the Cabinet

It took me about 100 rush calls to understand that many 'failed actuator' cases are really a power problem. The controller shows an alarm, but the issue is a loose connector, a blown fuse, or a voltage drop through an old cable.

Measure the actual voltage at the actuator's motor terminals while the command is on. If you only test at the cabinet disconnect, you'll miss the drop. This step feels too simple, and that's exactly why it's in the list.

Also check the holding brake. Some linear actuators have a brake that needs to release. If the brake doesn't open, the motor will draw current and eventually trip an overload. The actuator looks dead, but it's just locked.

Step 3: Pull the Datasheet Before You Pull the Motor

If power is good, the next question is: is the motor actually sized for the job? This is where you need the exact part number and the maxon motor datasheet for that series. As of January 2025, the fastest way to confirm a replacement is to download the datasheet for your exact part number, not to trust the number printed on a worn label.

I've lost count of how many times someone searched for 'maxon-motor' with a hyphen, or 'maxon motor datasheet', and then picked the first motor that looked similar. Don't. On a maxon motor datasheet, the critical values are torque constant, speed constant, terminal resistance, and the recommended operating range. Two motors with the same frame size can have completely different torque curves.

Open the datasheet and check:

  • Rated voltage and no-load speed
  • Continuous vs. intermittent torque
  • The torque-speed curve at your operating voltage
  • Gearbox ratio and maximum gearbox torque

The question everyone asks is, 'What is the part number?' The question they should ask is, 'What load was it carrying at the moment of failure?' (should mention: if you can't find the nameplate, take a photo and contact support before guessing.)

Step 4: Inspect the Mechanical Drive Train—Particularly the Timing Belt

This is the step that saves you from ordering a new motor when the real problem is a broken tooth or a loose tensioner. If your actuator uses a belt drive, a failed timing belt can look exactly like a motor failure. Motor spinning, no movement. Or the controller sees an encoder mismatch and stops.

Think about a Columbus timing belt replacement on a car: if the belt slips, the engine is still there, but the valves are in the wrong place. A linear actuator timing belt is the same in miniature. A worn or stretched belt can slip under load, trigger an error, and make you swear the motor is dead.

Check for:

  • Worn, cracked, or missing teeth on the belt
  • Tension—too loose causes slip; too tight destroys bearings (learned that one the expensive way)
  • Pulley condition—a worn pulley can kill a new belt quickly
  • Lead screw backlash if you're working on a screw-driven actuator

Here's the counterintuitive step: if the belt has been replaced before, don't trust the old tension setting. Belts get stiffer after they bed in. Replacing a belt is not the same as reusing the same belt. Always re-tension to the manufacturer's spec, not to 'how it felt before.'

Step 5: Decide—Repair, Replace, or Upgrade to a DC Servo Motor

Once you know whether the failure is electrical, mechanical, or the motor itself, you have three options:

  1. Repair—replace brushes, clean the commutator, or rebuild the gearbox. Good for low-cost equipment, but only if the winding and encoder are still healthy.
  2. Replace with the identical motor—fast and safe, but you're installing the same duty cycle that just failed.
  3. Upgrade to a brushless DC servo motor—more expensive today, but often the right call if the application runs continuously and the old motor was a consumable.

This is where the industry has evolved. The 'bigger motor is always better' thinking comes from an era when control options were limited. Today, a properly selected DC servo motor with closed-loop feedback can outperform a motor twice its size in a high-cycle application. What was best practice in 2020 may not apply in 2025.

If you decide to upgrade, go back to the maxon motor datasheet and check the duty cycle, not just the peak torque. And if you've been reading maxon motor news today, you know they've been pushing integrated drives and higher-voltage systems. That doesn't mean you need the newest thing. It means the options are better than they were a few years ago.

Step 6: Test With a Load Profile, Not Just an Empty Cycle

This is the step most people skip.

After you install the new motor or actuator, don't just jog it back and forth and call it done. You need to test it under the same load profile that caused the failure. Run the cycle with the actual product, or at least an equivalent load, for at least 30 minutes. More if the duty cycle is high.

Watch for:

  • Motor temperature—an infrared gun is fine for this
  • Current draw compared to the datasheet
  • Unusual noise or vibration
  • Position error or following error trends

If the motor gets too hot after 20 minutes, you have a sizing problem, not a defective part. (unfortunately, that's also the moment you discover whether you have enough cooling.)

I should add that we built a 48-hour buffer into our emergency repair policy after a 2023 incident. Missing a deadline would have meant a $50,000 penalty clause, so a two-day cushion is now standard. The extra time is not waste—it's an insurance premium.

Common Mistakes When Responding to an Actuator Failure

  • Ordering a replacement motor before taking a photo of the nameplate. The nameplate contains the exact voltage, current, and IP rating. A photo can save you a week.
  • Ignoring the controller's error history. The current alarm is rarely the first event; find the original fault.
  • Overtensioning a new timing belt. A tension that feels 'solid' can be too tight for the bearings. Use a tension gauge or the deflection method from the manual.
  • Choosing an intermittent-rated motor for continuous cycles. The datasheet may show a high torque for a few seconds, but the continuous rated torque is what keeps you running.

Bottom line: when a linear actuator fails, the answer is usually found in four places—power, load, motor sizing, and mechanical wear. Check them in that order. If you get to the end and the motor is truly dead, replace it with the correct part, not the closest one. And if this is the second failure of the same type in 12 months, treat it as a signal to upgrade. (note to self: always ask for the nameplate photo first—it's faster than chasing a part number by email.)